Sonic displacement transducer



Jan. 20, 1970 J. TELLERMAN Re. 26,774

SONIC DI SPLAC EMENT TRANSDUCER Original Filed July 20, 1966 2Sheets-Sheet 1 T- 5- .Z- f "1 @E50/v4 7- FREQUENCY Jan. 20, 1970 J.TELLERMAN Re. 26,774

SONIC DISPLACEMENT TRANSDUCER 2 Sheets-Sheet 2 Original Filed July 20.1906 /afe zag 30A: MA* 2J/r 60x 70x aan I HT/ ru /N FEE? United StatesPatent O 8 Int. Cl. G01t 7/12 U.S. Cl. 73-386 15 Claims Matter enclosedin heavy brackets appears in the original patent but forms no part ofthis reissue specification; matter prnted in italics indicates theadditions made by reissue.

ABSTRACT OF THE DISCLOSURE A displacement transducer utilizes an aneroidcapsule connected to opposite ends of a curved wire to cause capsuledisplacements to alter the curvature of the wire. Sonic reflectinglmasses are provided at opposite ends of the wire to define a sonicreverberation path through the wire, the masses being connected to thewalls of the capsule. Magnets are located at spaced points along thewire and are energized to produce torsional mode sound waves having aspeed of propagation through the wire that is a function of the wirecurvature and therefore of the capsule displacement. The speed ofpropagation is measured by determining the resonant oscillatingfrequency of the torsional sound waves in the reverberation path.

This invention relates to a displacement transducer, and morespecifically relates to a novel transducer for generating an electricalsignal in response to the change in the radius of curvature of a rodwhich causes a change in the velocity of sound in the rod.

It is known that the velocity of sonic waves in a curved rod will varyif the radius of curvature of the rod is changed.

In accordance with the present invention, which can have particularapplication to the measurement of the displacement of an aneroid capsulefor use, for example, in aircraft instruments, a curved wire is clampedat its both ends to large sonic reecting masses, at least one of whichis movable through a distance which is to be measured. This change inconfiguration of the wire will then change the velocity of sonic wavepropagation through the wire, and means are provided for measuringparameters functionally related to sonic wave progagation, thereby tomeasure the displacement of the end of the wire.

In accordance with one embodiment of the invention, the curved wirewhich can have any desired curvature such as a circular curvature or anS-shaped curvature, or the like, is forced into torsional resonancemode. The frequency of torsional resonance, which is related to thevelocity of sound propagation in the Wire, is then changed by varyingthe curvature of the wire by moving at least one of its ends over adistance which is to be measured. This will then change the frequency oftorsional resonance, even though the effective length of the wireremains constant.

In one embodiment of the invention, the reflecting blocks which receivethe ends of the wire are connected to the opposite walls of an aneroidcapsule used in aircraft-type instruments where the aneroid capsuleexpands or contracts responsive to pressure changes. This expansion andcontraction, which is a measure of the pressure differential applied tothe aneroid capsule, will then be reflected as varying torsionalresonance frequencies of the wire whose curvature is being adjusted bythe movement of the capsule walls. This frequency can then be displayedon a suitable indicator in digital form, if desired, thereby to form anextremely simple and highly accurate displacement measuring structurewhich could le calibrated in terms of air pressure differentials, or theike.

In order to cause the wire to oscillate in a torsional mode, anarrangement based on the so-called Wiedmann effect may be used, whereinthe rod is formed of a suitable ferromagnetic material which has anelectric current therethrough and also has a unidirectional magneticfield directed along the axis of the rod. If the current applied to therod is sinusoidal, the wire will oscillate about its axis with atorsional mode of oscillation. Suitable control circuitry can beprovided to cause the wire to oscillate at its resonant frequencythrough the use of a suitable regenerative circuit arrangement in whichthe frequency of the A-C cutter causing the torsional oscillation isadjusted by a suitable circuit means to the resonant torsional frequencyof the wire. A second circuit is then coupled to the torsionallyoscillating curved wire which uses the converse of the Wiedmann effecttransducer, wherein the wire is oscillated in a constant magnetic field,thereby to induce a Wiedmann current which can be used to control thedriving current frequency. Clearly, however, any suitable electricaldriving circuit could be used to sustain either torsional vibration ofthe wire or to directly measure the speed of sound in the wire as thewire curvature is changed to obtain a measure of the displacement of thewire ends.

Accordingly, a primary object of this invention is to provide a noveldisplacement transducer which can measure extremely small displacementswith high accuracy.

Another object of this invention is to provide a novel displacementtransducer which provides highly reproducible outputs for given inputmotions.

Still another object of this invention is to provide a noveldisplacement transducer especially adapted for use in aircraftinstruments for directly measuring the expansion or contraction of ananeroid capsule.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawings, inwhich:

FIGURE l schematically illustrates in perspective view a curve wire orrod terminating at either end on a respective sonic reflecting mass, oneof which is movable.

FIGURE 2 is a modification of the arrangement of FIGURE l wherein thecurved rod has an S-shape rather than the circular shape of FIGURE l.

FIGURE 3 illustrates the manner in which a permanent magnet and voltagesource can be connected to the wire of FIGURE 3 to cause it to oscillatein a torsional mode of oscillation by virtue of the Wiedmann effect.

FIGURE 4 is a similar to FIGURE 3 and illustrates the placement of apickoff circuit which is regeneratively connected to an amplifiersupplying the current which causes the rod to oscillate in its torsionalmode.

FIGURE 5 is a top plan view of an aneroid capsule which is connected tovary the curvature of a rod of the type shown in FIGURE 4.

FIGURE 6 is a cross-sectional view of FIGURE 5 taken across the lines6-6 in FIGURE 5.

FIGURE 7 illustrates altitude pressure as a function of frequency changefor the arrangement of FIGURES 5 and 6.

Referring first to FIGURE 1, there is illustrated therein a curved rod10 of a sound conductive material which is clamped at either end to thesonic reflecting masses 11 and 12. Mass 11 is shown as a fixed mass,while the mass 12 is shown as being movable toward or away from mass 1lin the direction of arrow 13, thereby to alter the curvature of rod l0.

In accordance with the invention, and recognizing that the velocity ofsound through rod 10 will change with a change in curvature of rod 10,means are connected to rod l for measuring the sonic velocity thereinwhich will be functionally related to the curvature of rod 10, and thusthe position of reflecting mass 12.

One manner in which this measurement can be made is schematicallyillustrated in FIGURE 1 by block 14 connected to rod and adapted tooscillate rod l0 about its axis in a torsional reso-nance mode. Asuitable frequency measuring means for measuring the resonant frequencyof rod 10 is then provided by block 15 which could take any desiredform.

In operation, a change in position of reflecting block 12 will changethe speed of sound in rod 10 and will thereby change its torsionalresonance frequency. Therefore, a measurement of the torsional resonancefrequency will be related to the position of mass 12.

While FIGURE 1 illustrates the invention for a circularly curved rod 10,it should be understood that any curvature could be used. For example,FIGURE 2 illustrates the use of an S-shaped rod which is clamped betweena fixed reflecting block 21 and a movable reflecting block 22 which ismovable in the direction of arrow 23. Once again, as the block 22 ismoved, the speed of sound in rod 20 and thus its torsional resonancefrequency will be changed, with this change measurable by the resonantfrequency measuring means 15.

One manner in which torsional resonance can be induced in the rod 20 isillustrated in FIGURE 3 which shows the application of a Wiedmann effecttype arrangement to the structure of FIGURE l.

In accordance with the Wiedmann effect, a ferromagt netic rod can bemechanically twisted by introducing an electric current through the rodand a magnetic field along the axis of the rod. Thus, a twisting ortorsional force can be introduced into one half of wire 10 by connectinga suitable voltage source in series with the left-hand portion of wire10 and by placing a permanent magnet 31 adjacent wire 10 such that amagnetic flux will be directed along the axis of wire 10 and parallel tothe flow of current through wire 10 from source 30. Note that wire 10may be of any ferromagnetic material, and good results have beenobtained when using a wire of Ni-Span C material.

A frequency measuring means 32 connected to the bar will then measure afrequency of torsional oscillation which is functionally related to thetorsional oscillation frequency of wire 10.

In order to sustain oscillation in the bar l0, a voltage pickoff orsuitable mechanical-to-electrical converter can be provided which isregeneratively applied to the torsional resonance driving circuitincluding members 30 and 31 of FIGURE 3.

This is illustrated in FIGURE 4 where components similar to those ofFIGURE 3 have similar identifying numerals. In FIGURE 4, however, thevoltage source 30 of FIGURE 3 is replaced by a suitable variablefrequency amplifier 39 having output conductors 40 and 41 connected tothe left half portion of rod 10. Variable frequency amplifier 39 thenhas input conductors 42 and 43 which control its output frequency withconductors 42 and 43 connected to a portion of wire 10 removed from theelectrical circuit included in the output conductors and 41.

A second permanent magnet 44 is then arranged parallel to this secondportion of rod 10, whereby magnet 44 and a torsionally oscillatingportion of wire 10 adjacent thereto will induce a Wiedmann current inthis portion of wire 10 which is connected to terminals 42 and 43.Therefore, the wire l0, which attempts to oscillate at its resonantfrequency, will deliver a signal to the input of amplifier 39 over inputconductors 42 and 43 which will cause amplifier 39 to adjust its outputfrequency until the output current at conductors 40 and 41 along withmagnet 31 will always drive wire l0 at its resonant torsional frequency.

This resonant torsional frequency, however, will be dependent upon theparticular displacement of reflecting mass 12, and thus the curvature ofrod 10, so that the output frequency of amplifier 39 will befunctionally related to the displacement of mass l2.

FIGURES 5 and 6 illustrate the application of the present invention tothe measurement of the deflection of` the walls of the aneroid capsule.Referring now to FIG- URES 5 and 6, there is illustrated therein asupport platform 50 which mounts an aneroid capsule 5l at its rim S2.The opposing walls of capsule 51 are free to expand and contract withvarying conditions of differential pressure, and the center of theopposing walls carry sonic refleeting masses 53 and 54 which can takethe shape of clamping blocks for clamping the two ends of curved rod 5S.

More particularly, and as shown in FIGURE 6 for the case of reflectingmass 53, it will be seen that the mass 53 can be formed of two halves 56and 57 which are clampable to the end of rod 55 by the clamping bolts 58and 59.

Suitable terminals 60, 61 and 62 are then provided at each end of rod 55and at the center of rod 55 for counection to a suitable driving andfrequency measuring circuit in a manner similar to that shown in FIGURE4. Suitable permanent magnets such as permanent magnet 63 are providedas needed, as illustrated in FIGURE 4.

In the embodiment of FIGURES 5 and 6, the circularly arranged rod 55 wasformed of Ni-Span C wire having a diameter of .020 inch, a length of7*/2 inches and bent to a radius of approximately 1735i; inches. Theclamps 53 and 54 are constructed of brass and have a mass ofapproximately 2 grams and a size of about ift/n1" x ,f'ln" x lit. Astandard beryllium copper diaphragm used in aircraft instruments formeasurement of pressure altitudes of from zero to 80,000 feet was usedfor the aneroid capsule 51. Pressure differentials corresponding toaltitude changes from zero to 80,000 feet in altitude were then appliedto capsule 5l, and the frequency change in torsional rotation of bar 55was measured from a reference frequency of 37,481 cycles per second.That is to say, the driving current connected between terminals 61 and62 and the field strength of magnet 63 were initially adjusted to causeoscillation of rod 55, which was in an unstrained State when capsule 51was at its sea-level altitude pressure, at 37,481 cycles per second. Thepressure surrounding capsule 51 was then decreased to a pressurecorresponding to 80,000 feet in altitude, and the capsule walls extendedproportionally thereby moving clamping members 53 and 54 away from oneanother to increase the radius of bar 55.

The frequency change measured for the torsional resonant frequency ofrod 55 from zero to 80,000 feet is illustrated in FIGURE 7 where it isseen that a total frequency change of approximately 900 cycles from thereference frequency was measured. This frequency change was applied to adigital frequency meter which was calibrated in terms of altitude,whereby the entire instrument was useful as an altimeter having highlyreproducible readings with a minimum of moving parts.

Although this invention has been described with rcspect to its preferredembodiments, it should be understood that many variations andmodifications will now be obvious to those skilled in the art, and it ispreferred, therefore, that the scope of the invention be limited not bythe specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed arc defined as follows:

1. A displacement transducer comprising a self-supporting resilientcurved rod having a rst and second end; u rst and second sonic reectingmass connected to said first and second ends, respectively; means formoving said first and second sonic reflecting masses with respect to oneanother to alter the curvature of said curved rod; and means formeasuring the speed of sound in said rod connected to said rod; therelative displacement between said first and second sonic reflectingmasses being unctionally related to the speed of sound in said rod.

2. The device as set forth in claim 1 wherein said means for measuringthe speed of sound in said rod includes means for inducing the torsionaloscillation of said rod at its resonant oscillating frequency and meansfor measuring said oscillating frequency.

3. The device as set forth in claim 2 wherein said means for inducingtorsional oscillation of said rod includes magnet means for passing amagnetic eld through at least a portion of said rod and means forpassing an adjustable frequency alternating current through said portionof said rod; said rod constructed of ferromagnetic material.

4. The device as set forth in claim 3 which includes second magnet meansfor introducing a magnetic eld into a second portion of said rod andcircuit means connected to said second portion of said rod receiving aninduced current having the frequency of oscillation of said rod; andregenerative circuit means connecting said circuit means to said meansfor passing an adjustable frequency alternating current through saidportion of said rod to adjust said adjustable frequency to the resonantfrequency of said rod.

5. The device as set forth in claim 4 wherein at least one of said firstand second sonic masses is connected to the wall of an aneroid capsule.

6. The device as set forth in claim 1 wherein at least one of said firstand second sonic masses is connected to the Wall of an aneroid capsule.

7. The device as set forth in claim 1 wherein said rod is circularlycurved.

8. The device as set forth in claim 1 wherein said rod is curved in theform of an S-shape.

9. A displacement transducer comprising an element of resilient rod-likematerial having a predetermined curved shape and having sonic reflectingmeans thereon to establish a reverberation path through the element,movable displacement means for altering the curvature of n rod portionof said element that is in said path, and means for measuring the speedof propagation of torsional mode sound waves through said rod portion usa function 0f a movement of said displacement means.

10. A displacement transducer in accordance with claim 9 and whereinsaid means for measuring speed includes means for inducing torsionaloscillation of said rod portion nt its resonant oscillating frequencyand means for measuring said resonant oscillating frequency.

ll. A displacement transducer in accordance with claim 9 and whereinsaid rod portion is of ferromagnetic material and said means formeasuring speed includes means for inducing torsional oscillationcomprising first magnet means providing a magnetic field through atleast cz region of said rod portion and means for passing un adjustablefrequency alternating current through said region of said rod.

l2. A displacement transducer in accordance with claim ll and includingsecond magnet means for providing n magnetic held through another regionof said I'Od portion., first circuit means coupled to the last-namedregion of said rod portion to receive an induced current at thefrequency of oscillation of said rod portion and regenerative circuitmeans connecting said 1trst circuit means to said means for passing toadjust the frequency of said alternating current to the resonantfrequency of said rod portion.

13. A displacement transducer in accordance with claim 9 and whereinsaid movable displacement means in cludes a wall of an aneroid capsule.

14. A displacement transducer in accordance with claim 9 and whereinsaid rod portion is circularly curved.

15. A displacement transducer comprising an element 0f resilientrod-like material having a predetermined curved shape; sonic reflectingmeans on the element to define a reverberation path through the rod-likeelement; means coupled to the rod-like element for producing torsionalsound waves propagating therethrough; movable displacement means coupledto the rod-like element for altering the curved shape of said element;and means responsive to the torsional sound ware propagating through theelement for producing a signal that varies in accordance with the speedof propagation of such waves.

References Cited The following references cited by the Examiner, are ofrecord in the patented lile of this patent or the original patent.

UNITED STATES PATENTS 3,101,001 8/1963 Appleton 73-517 XR 3,327,5336/1967 Kooiman 73-398 3,257,850 6/1966 Kooiman 73-398 DONALD O. WOODIEL,Primary Examiner U.S. Cl. X-R. 73-398

